错误TS2365：运算符'！=='无法应用于类型'“（”'和'“）”'

发生的是类型变窄。在传递第一个if语句之后，将类型限制id为字符串文字“）”，因为否则将引发异常。

function myFunc(id: string) {
  id = "(";
};
// Note that this function does nothing, but it's not the issue here

let id: string = ")";

if (id !== '(')
  throw "Expected '(' in prototype";
// id is narrowed to "("

myFunc(id);

// now id and ')' does not have same type, hence the error
if (id !== ')')
  throw "Expected ')' in prototype";